The invention relates to a hand wheel actuator for a steer-by-wire system of an automobile.
Automobiles are conventionally equipped with a pair of front road wheels that are steered to enable the vehicle to turn left and right as it maneuvers on land. It is also known to provide actuators for steering rear wheels in automobiles. In the past, vehicle steering systems commonly employed a mechanical connection between the driver-operated hand wheel and the front road wheels of an automotive vehicle. As the driver rotated the hand wheel, a mechanical linkage through the vehicle""s tie-rods actuated the road wheels sometimes with the assistance of a power assist steering motor or hydraulic piston.
Recently, steer-by-wire steering systems have been introduced into automotive vehicles to provide road wheel steering function. Included in a typical steer-by-wire steering system is a hand wheel actuator for monitoring the angular position of the steering wheel, and road wheel motor actuators which are controlled by controllers in response to tracking the sensed angular displacement of the hand wheel from a central position. In contrast to prior steering systems, the steer-by-wire steering system does not employ a mechanical linkage between the steering wheel and the individual road wheels. Exemplary of such known steer-by-wire systems is commonly-assigned U.S. Pat. No. 6,176,341, issued Jan. 23, 20001 to Ansari.
Because there is no mechanical linkage between the hand wheel and road wheels in a steer-by-wire system, steering enhancements such as variable-ratio steering are easily implemented to improve the drivability of the vehicle. However, when variable-ratio steering is implemented, the extreme left and extreme right limits of steering do not consistently correspond with the extreme left and extreme right limits of the road wheels. For example, if the hand to road wheel steering ratio is decreased for traveling at low speeds, e.g., in a parking lot situation, the driver need not rotate the hand wheel as far as he or she would if variable ratio steering was not implemented. In this case, the road wheels will reach the limit of their steering capability before the hand wheel does since the positive travel end stop is fixed to correspond with the highest hand wheel to road wheel turning ratio. It would therefore be desirable to provide feedback to the driver when the road wheels have reached their steering limit. Ideally, such a mechanism would allow the variable ratio steering to stop the travel of the hand-wheel at any point where the road wheels have reached their steering limit.
The above-discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by providing a hand wheel actuator for providing force feedback to a user. The actuator comprises a steering shaft that is supported by bearings and has an end suitable for attaching a hand wheel thereto; a position sensor detecting the angular displacement of the steering shaft from a central position and producing a signal indicative of such angular displacement; an electric motor and a transmission applying torque to the steering shaft to provide force-feedback to a user; and a variable stopper configured to stop rotation of the steering shaft at an arbitrary location. The above-discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings.